ulpqueue.c

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/* SCTP kernel implementation
 * (C) Copyright IBM Corp. 2001, 2004
 * Copyright (c) 1999-2000 Cisco, Inc.
 * Copyright (c) 1999-2001 Motorola, Inc.
 * Copyright (c) 2001 Intel Corp.
 * Copyright (c) 2001 Nokia, Inc.
 * Copyright (c) 2001 La Monte H.P. Yarroll
 *
 * This abstraction carries sctp events to the ULP (sockets).
 *
 * This SCTP implementation is free software;
 * you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This SCTP implementation is distributed in the hope that it
 * will be useful, but WITHOUT ANY WARRANTY; without even the implied
 *                 ************************
 * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with GNU CC; see the file COPYING.  If not, write to
 * the Free Software Foundation, 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * Please send any bug reports or fixes you make to the
 * email address(es):
 *    lksctp developers <[email protected]>
 *
 * Or submit a bug report through the following website:
 *    http://www.sf.net/projects/lksctp
 *
 * Written or modified by:
 *    Jon Grimm             <[email protected]>
 *    La Monte H.P. Yarroll <[email protected]>
 *    Sridhar Samudrala     <[email protected]>
 *
 * Any bugs reported given to us we will try to fix... any fixes shared will
 * be incorporated into the next SCTP release.
 */

#include <linux/slab.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <net/sock.h>
#include <net/sctp/structs.h>
#include <net/sctp/sctp.h>
#include <net/sctp/sm.h>

/* Forward declarations for internal helpers.  */
static struct sctp_ulpevent * sctp_ulpq_reasm(struct sctp_ulpq *ulpq,
                          struct sctp_ulpevent *);
static struct sctp_ulpevent * sctp_ulpq_order(struct sctp_ulpq *,
                          struct sctp_ulpevent *);
static void sctp_ulpq_reasm_drain(struct sctp_ulpq *ulpq);

/* 1st Level Abstractions */

/* Initialize a ULP queue from a block of memory.  */
struct sctp_ulpq *sctp_ulpq_init(struct sctp_ulpq *ulpq,
                 struct sctp_association *asoc)
{
    memset(ulpq, 0, sizeof(struct sctp_ulpq));

    ulpq->asoc = asoc;
    skb_queue_head_init(&ulpq->reasm);
    skb_queue_head_init(&ulpq->lobby);
    ulpq->pd_mode  = 0;
    ulpq->malloced = 0;

    return ulpq;
}


/* Flush the reassembly and ordering queues.  */
void sctp_ulpq_flush(struct sctp_ulpq *ulpq)
{
    struct sk_buff *skb;
    struct sctp_ulpevent *event;

    while ((skb = __skb_dequeue(&ulpq->lobby)) != NULL) {
        event = sctp_skb2event(skb);
        sctp_ulpevent_free(event);
    }

    while ((skb = __skb_dequeue(&ulpq->reasm)) != NULL) {
        event = sctp_skb2event(skb);
        sctp_ulpevent_free(event);
    }

}

/* Dispose of a ulpqueue.  */
void sctp_ulpq_free(struct sctp_ulpq *ulpq)
{
    sctp_ulpq_flush(ulpq);
    if (ulpq->malloced)
        kfree(ulpq);
}

/* Process an incoming DATA chunk.  */
int sctp_ulpq_tail_data(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
            gfp_t gfp)
{
    struct sk_buff_head temp;
    struct sctp_ulpevent *event;

    /* Create an event from the incoming chunk. */
    event = sctp_ulpevent_make_rcvmsg(chunk->asoc, chunk, gfp);
    if (!event)
        return -ENOMEM;

    /* Do reassembly if needed.  */
    event = sctp_ulpq_reasm(ulpq, event);

    /* Do ordering if needed.  */
    if ((event) && (event->msg_flags & MSG_EOR)){
        /* Create a temporary list to collect chunks on.  */
        skb_queue_head_init(&temp);
        __skb_queue_tail(&temp, sctp_event2skb(event));

        event = sctp_ulpq_order(ulpq, event);
    }

    /* Send event to the ULP.  'event' is the sctp_ulpevent for
     * very first SKB on the 'temp' list.
     */
    if (event)
        sctp_ulpq_tail_event(ulpq, event);

    return 0;
}

/* Add a new event for propagation to the ULP.  */
/* Clear the partial delivery mode for this socket.   Note: This
 * assumes that no association is currently in partial delivery mode.
 */
int sctp_clear_pd(struct sock *sk, struct sctp_association *asoc)
{
    struct sctp_sock *sp = sctp_sk(sk);

    if (atomic_dec_and_test(&sp->pd_mode)) {
        /* This means there are no other associations in PD, so
         * we can go ahead and clear out the lobby in one shot
         */
        if (!skb_queue_empty(&sp->pd_lobby)) {
            struct list_head *list;
            sctp_skb_list_tail(&sp->pd_lobby, &sk->sk_receive_queue);
            list = (struct list_head *)&sctp_sk(sk)->pd_lobby;
            INIT_LIST_HEAD(list);
            return 1;
        }
    } else {
        /* There are other associations in PD, so we only need to
         * pull stuff out of the lobby that belongs to the
         * associations that is exiting PD (all of its notifications
         * are posted here).
         */
        if (!skb_queue_empty(&sp->pd_lobby) && asoc) {
            struct sk_buff *skb, *tmp;
            struct sctp_ulpevent *event;

            sctp_skb_for_each(skb, &sp->pd_lobby, tmp) {
                event = sctp_skb2event(skb);
                if (event->asoc == asoc) {
                    __skb_unlink(skb, &sp->pd_lobby);
                    __skb_queue_tail(&sk->sk_receive_queue,
                             skb);
                }
            }
        }
    }

    return 0;
}

/* Set the pd_mode on the socket and ulpq */
static void sctp_ulpq_set_pd(struct sctp_ulpq *ulpq)
{
    struct sctp_sock *sp = sctp_sk(ulpq->asoc->base.sk);

    atomic_inc(&sp->pd_mode);
    ulpq->pd_mode = 1;
}

/* Clear the pd_mode and restart any pending messages waiting for delivery. */
static int sctp_ulpq_clear_pd(struct sctp_ulpq *ulpq)
{
    ulpq->pd_mode = 0;
    sctp_ulpq_reasm_drain(ulpq);
    return sctp_clear_pd(ulpq->asoc->base.sk, ulpq->asoc);
}

/* If the SKB of 'event' is on a list, it is the first such member
 * of that list.
 */
int sctp_ulpq_tail_event(struct sctp_ulpq *ulpq, struct sctp_ulpevent *event)
{
    struct sock *sk = ulpq->asoc->base.sk;
    struct sk_buff_head *queue, *skb_list;
    struct sk_buff *skb = sctp_event2skb(event);
    int clear_pd = 0;

    skb_list = (struct sk_buff_head *) skb->prev;

    /* If the socket is just going to throw this away, do not
     * even try to deliver it.
     */
    if (sock_flag(sk, SOCK_DEAD) || (sk->sk_shutdown & RCV_SHUTDOWN))
        goto out_free;

    /* Check if the user wishes to receive this event.  */
    if (!sctp_ulpevent_is_enabled(event, &sctp_sk(sk)->subscribe))
        goto out_free;

    /* If we are in partial delivery mode, post to the lobby until
     * partial delivery is cleared, unless, of course _this_ is
     * the association the cause of the partial delivery.
     */

    if (atomic_read(&sctp_sk(sk)->pd_mode) == 0) {
        queue = &sk->sk_receive_queue;
    } else {
        if (ulpq->pd_mode) {
            /* If the association is in partial delivery, we
             * need to finish delivering the partially processed
             * packet before passing any other data.  This is
             * because we don't truly support stream interleaving.
             */
            if ((event->msg_flags & MSG_NOTIFICATION) ||
                (SCTP_DATA_NOT_FRAG ==
                    (event->msg_flags & SCTP_DATA_FRAG_MASK)))
                queue = &sctp_sk(sk)->pd_lobby;
            else {
                clear_pd = event->msg_flags & MSG_EOR;
                queue = &sk->sk_receive_queue;
            }
        } else {
            /*
             * If fragment interleave is enabled, we
             * can queue this to the receive queue instead
             * of the lobby.
             */
            if (sctp_sk(sk)->frag_interleave)
                queue = &sk->sk_receive_queue;
            else
                queue = &sctp_sk(sk)->pd_lobby;
        }
    }

    /* If we are harvesting multiple skbs they will be
     * collected on a list.
     */
    if (skb_list)
        sctp_skb_list_tail(skb_list, queue);
    else
        __skb_queue_tail(queue, skb);

    /* Did we just complete partial delivery and need to get
     * rolling again?  Move pending data to the receive
     * queue.
     */
    if (clear_pd)
        sctp_ulpq_clear_pd(ulpq);

    if (queue == &sk->sk_receive_queue)
        sk->sk_data_ready(sk, 0);
    return 1;

out_free:
    if (skb_list)
        sctp_queue_purge_ulpevents(skb_list);
    else
        sctp_ulpevent_free(event);

    return 0;
}

/* 2nd Level Abstractions */

/* Helper function to store chunks that need to be reassembled.  */
static void sctp_ulpq_store_reasm(struct sctp_ulpq *ulpq,
                     struct sctp_ulpevent *event)
{
    struct sk_buff *pos;
    struct sctp_ulpevent *cevent;
    __u32 tsn, ctsn;

    tsn = event->tsn;

    /* See if it belongs at the end. */
    pos = skb_peek_tail(&ulpq->reasm);
    if (!pos) {
        __skb_queue_tail(&ulpq->reasm, sctp_event2skb(event));
        return;
    }

    /* Short circuit just dropping it at the end. */
    cevent = sctp_skb2event(pos);
    ctsn = cevent->tsn;
    if (TSN_lt(ctsn, tsn)) {
        __skb_queue_tail(&ulpq->reasm, sctp_event2skb(event));
        return;
    }

    /* Find the right place in this list. We store them by TSN.  */
    skb_queue_walk(&ulpq->reasm, pos) {
        cevent = sctp_skb2event(pos);
        ctsn = cevent->tsn;

        if (TSN_lt(tsn, ctsn))
            break;
    }

    /* Insert before pos. */
    __skb_queue_before(&ulpq->reasm, pos, sctp_event2skb(event));

}

/* Helper function to return an event corresponding to the reassembled
 * datagram.
 * This routine creates a re-assembled skb given the first and last skb's
 * as stored in the reassembly queue. The skb's may be non-linear if the sctp
 * payload was fragmented on the way and ip had to reassemble them.
 * We add the rest of skb's to the first skb's fraglist.
 */
static struct sctp_ulpevent *sctp_make_reassembled_event(struct net *net,
    struct sk_buff_head *queue, struct sk_buff *f_frag,
    struct sk_buff *l_frag)
{
    struct sk_buff *pos;
    struct sk_buff *new = NULL;
    struct sctp_ulpevent *event;
    struct sk_buff *pnext, *last;
    struct sk_buff *list = skb_shinfo(f_frag)->frag_list;

    /* Store the pointer to the 2nd skb */
    if (f_frag == l_frag)
        pos = NULL;
    else
        pos = f_frag->next;

    /* Get the last skb in the f_frag's frag_list if present. */
    for (last = list; list; last = list, list = list->next);

    /* Add the list of remaining fragments to the first fragments
     * frag_list.
     */
    if (last)
        last->next = pos;
    else {
        if (skb_cloned(f_frag)) {
            /* This is a cloned skb, we can't just modify
             * the frag_list.  We need a new skb to do that.
             * Instead of calling skb_unshare(), we'll do it
             * ourselves since we need to delay the free.
             */
            new = skb_copy(f_frag, GFP_ATOMIC);
            if (!new)
                return NULL;    /* try again later */

            sctp_skb_set_owner_r(new, f_frag->sk);

            skb_shinfo(new)->frag_list = pos;
        } else
            skb_shinfo(f_frag)->frag_list = pos;
    }

    /* Remove the first fragment from the reassembly queue.  */
    __skb_unlink(f_frag, queue);

    /* if we did unshare, then free the old skb and re-assign */
    if (new) {
        kfree_skb(f_frag);
        f_frag = new;
    }

    while (pos) {

        pnext = pos->next;

        /* Update the len and data_len fields of the first fragment. */
        f_frag->len += pos->len;
        f_frag->data_len += pos->len;

        /* Remove the fragment from the reassembly queue.  */
        __skb_unlink(pos, queue);

        /* Break if we have reached the last fragment.  */
        if (pos == l_frag)
            break;
        pos->next = pnext;
        pos = pnext;
    }

    event = sctp_skb2event(f_frag);
    SCTP_INC_STATS(net, SCTP_MIB_REASMUSRMSGS);

    return event;
}


/* Helper function to check if an incoming chunk has filled up the last
 * missing fragment in a SCTP datagram and return the corresponding event.
 */
static struct sctp_ulpevent *sctp_ulpq_retrieve_reassembled(struct sctp_ulpq *ulpq)
{
    struct sk_buff *pos;
    struct sctp_ulpevent *cevent;
    struct sk_buff *first_frag = NULL;
    __u32 ctsn, next_tsn;
    struct sctp_ulpevent *retval = NULL;
    struct sk_buff *pd_first = NULL;
    struct sk_buff *pd_last = NULL;
    size_t pd_len = 0;
    struct sctp_association *asoc;
    u32 pd_point;

    /* Initialized to 0 just to avoid compiler warning message.  Will
     * never be used with this value. It is referenced only after it
     * is set when we find the first fragment of a message.
     */
    next_tsn = 0;

    /* The chunks are held in the reasm queue sorted by TSN.
     * Walk through the queue sequentially and look for a sequence of
     * fragmented chunks that complete a datagram.
     * 'first_frag' and next_tsn are reset when we find a chunk which
     * is the first fragment of a datagram. Once these 2 fields are set
     * we expect to find the remaining middle fragments and the last
     * fragment in order. If not, first_frag is reset to NULL and we
     * start the next pass when we find another first fragment.
     *
     * There is a potential to do partial delivery if user sets
     * SCTP_PARTIAL_DELIVERY_POINT option. Lets count some things here
     * to see if can do PD.
     */
    skb_queue_walk(&ulpq->reasm, pos) {
        cevent = sctp_skb2event(pos);
        ctsn = cevent->tsn;

        switch (cevent->msg_flags & SCTP_DATA_FRAG_MASK) {
        case SCTP_DATA_FIRST_FRAG:
            /* If this "FIRST_FRAG" is the first
             * element in the queue, then count it towards
             * possible PD.
             */
            if (pos == ulpq->reasm.next) {
                pd_first = pos;
                pd_last = pos;
                pd_len = pos->len;
            } else {
                pd_first = NULL;
                pd_last = NULL;
                pd_len = 0;
            }

            first_frag = pos;
            next_tsn = ctsn + 1;
            break;

        case SCTP_DATA_MIDDLE_FRAG:
            if ((first_frag) && (ctsn == next_tsn)) {
                next_tsn++;
                if (pd_first) {
                    pd_last = pos;
                    pd_len += pos->len;
                }
            } else
                first_frag = NULL;
            break;

        case SCTP_DATA_LAST_FRAG:
            if (first_frag && (ctsn == next_tsn))
                goto found;
            else
                first_frag = NULL;
            break;
        }
    }

    asoc = ulpq->asoc;
    if (pd_first) {
        /* Make sure we can enter partial deliver.
         * We can trigger partial delivery only if framgent
         * interleave is set, or the socket is not already
         * in  partial delivery.
         */
        if (!sctp_sk(asoc->base.sk)->frag_interleave &&
            atomic_read(&sctp_sk(asoc->base.sk)->pd_mode))
            goto done;

        cevent = sctp_skb2event(pd_first);
        pd_point = sctp_sk(asoc->base.sk)->pd_point;
        if (pd_point && pd_point <= pd_len) {
            retval = sctp_make_reassembled_event(sock_net(asoc->base.sk),
                                 &ulpq->reasm,
                                 pd_first,
                                 pd_last);
            if (retval)
                sctp_ulpq_set_pd(ulpq);
        }
    }
done:
    return retval;
found:
    retval = sctp_make_reassembled_event(sock_net(ulpq->asoc->base.sk),
                         &ulpq->reasm, first_frag, pos);
    if (retval)
        retval->msg_flags |= MSG_EOR;
    goto done;
}

/* Retrieve the next set of fragments of a partial message. */
static struct sctp_ulpevent *sctp_ulpq_retrieve_partial(struct sctp_ulpq *ulpq)
{
    struct sk_buff *pos, *last_frag, *first_frag;
    struct sctp_ulpevent *cevent;
    __u32 ctsn, next_tsn;
    int is_last;
    struct sctp_ulpevent *retval;

    /* The chunks are held in the reasm queue sorted by TSN.
     * Walk through the queue sequentially and look for the first
     * sequence of fragmented chunks.
     */

    if (skb_queue_empty(&ulpq->reasm))
        return NULL;

    last_frag = first_frag = NULL;
    retval = NULL;
    next_tsn = 0;
    is_last = 0;

    skb_queue_walk(&ulpq->reasm, pos) {
        cevent = sctp_skb2event(pos);
        ctsn = cevent->tsn;

        switch (cevent->msg_flags & SCTP_DATA_FRAG_MASK) {
        case SCTP_DATA_MIDDLE_FRAG:
            if (!first_frag) {
                first_frag = pos;
                next_tsn = ctsn + 1;
                last_frag = pos;
            } else if (next_tsn == ctsn)
                next_tsn++;
            else
                goto done;
            break;
        case SCTP_DATA_LAST_FRAG:
            if (!first_frag)
                first_frag = pos;
            else if (ctsn != next_tsn)
                goto done;
            last_frag = pos;
            is_last = 1;
            goto done;
        default:
            return NULL;
        }
    }

    /* We have the reassembled event. There is no need to look
     * further.
     */
done:
    retval = sctp_make_reassembled_event(sock_net(ulpq->asoc->base.sk),
                    &ulpq->reasm, first_frag, last_frag);
    if (retval && is_last)
        retval->msg_flags |= MSG_EOR;

    return retval;
}


/* Helper function to reassemble chunks.  Hold chunks on the reasm queue that
 * need reassembling.
 */
static struct sctp_ulpevent *sctp_ulpq_reasm(struct sctp_ulpq *ulpq,
                        struct sctp_ulpevent *event)
{
    struct sctp_ulpevent *retval = NULL;

    /* Check if this is part of a fragmented message.  */
    if (SCTP_DATA_NOT_FRAG == (event->msg_flags & SCTP_DATA_FRAG_MASK)) {
        event->msg_flags |= MSG_EOR;
        return event;
    }

    sctp_ulpq_store_reasm(ulpq, event);
    if (!ulpq->pd_mode)
        retval = sctp_ulpq_retrieve_reassembled(ulpq);
    else {
        __u32 ctsn, ctsnap;

        /* Do not even bother unless this is the next tsn to
         * be delivered.
         */
        ctsn = event->tsn;
        ctsnap = sctp_tsnmap_get_ctsn(&ulpq->asoc->peer.tsn_map);
        if (TSN_lte(ctsn, ctsnap))
            retval = sctp_ulpq_retrieve_partial(ulpq);
    }

    return retval;
}

/* Retrieve the first part (sequential fragments) for partial delivery.  */
static struct sctp_ulpevent *sctp_ulpq_retrieve_first(struct sctp_ulpq *ulpq)
{
    struct sk_buff *pos, *last_frag, *first_frag;
    struct sctp_ulpevent *cevent;
    __u32 ctsn, next_tsn;
    struct sctp_ulpevent *retval;

    /* The chunks are held in the reasm queue sorted by TSN.
     * Walk through the queue sequentially and look for a sequence of
     * fragmented chunks that start a datagram.
     */

    if (skb_queue_empty(&ulpq->reasm))
        return NULL;

    last_frag = first_frag = NULL;
    retval = NULL;
    next_tsn = 0;

    skb_queue_walk(&ulpq->reasm, pos) {
        cevent = sctp_skb2event(pos);
        ctsn = cevent->tsn;

        switch (cevent->msg_flags & SCTP_DATA_FRAG_MASK) {
        case SCTP_DATA_FIRST_FRAG:
            if (!first_frag) {
                first_frag = pos;
                next_tsn = ctsn + 1;
                last_frag = pos;
            } else
                goto done;
            break;

        case SCTP_DATA_MIDDLE_FRAG:
            if (!first_frag)
                return NULL;
            if (ctsn == next_tsn) {
                next_tsn++;
                last_frag = pos;
            } else
                goto done;
            break;
        default:
            return NULL;
        }
    }

    /* We have the reassembled event. There is no need to look
     * further.
     */
done:
    retval = sctp_make_reassembled_event(sock_net(ulpq->asoc->base.sk),
                    &ulpq->reasm, first_frag, last_frag);
    return retval;
}

/*
 * Flush out stale fragments from the reassembly queue when processing
 * a Forward TSN.
 *
 * RFC 3758, Section 3.6
 *
 * After receiving and processing a FORWARD TSN, the data receiver MUST
 * take cautions in updating its re-assembly queue.  The receiver MUST
 * remove any partially reassembled message, which is still missing one
 * or more TSNs earlier than or equal to the new cumulative TSN point.
 * In the event that the receiver has invoked the partial delivery API,
 * a notification SHOULD also be generated to inform the upper layer API
 * that the message being partially delivered will NOT be completed.
 */
void sctp_ulpq_reasm_flushtsn(struct sctp_ulpq *ulpq, __u32 fwd_tsn)
{
    struct sk_buff *pos, *tmp;
    struct sctp_ulpevent *event;
    __u32 tsn;

    if (skb_queue_empty(&ulpq->reasm))
        return;

    skb_queue_walk_safe(&ulpq->reasm, pos, tmp) {
        event = sctp_skb2event(pos);
        tsn = event->tsn;

        /* Since the entire message must be abandoned by the
         * sender (item A3 in Section 3.5, RFC 3758), we can
         * free all fragments on the list that are less then
         * or equal to ctsn_point
         */
        if (TSN_lte(tsn, fwd_tsn)) {
            __skb_unlink(pos, &ulpq->reasm);
            sctp_ulpevent_free(event);
        } else
            break;
    }
}

/*
 * Drain the reassembly queue.  If we just cleared parted delivery, it
 * is possible that the reassembly queue will contain already reassembled
 * messages.  Retrieve any such messages and give them to the user.
 */
static void sctp_ulpq_reasm_drain(struct sctp_ulpq *ulpq)
{
    struct sctp_ulpevent *event = NULL;
    struct sk_buff_head temp;

    if (skb_queue_empty(&ulpq->reasm))
        return;

    while ((event = sctp_ulpq_retrieve_reassembled(ulpq)) != NULL) {
        /* Do ordering if needed.  */
        if ((event) && (event->msg_flags & MSG_EOR)){
            skb_queue_head_init(&temp);
            __skb_queue_tail(&temp, sctp_event2skb(event));

            event = sctp_ulpq_order(ulpq, event);
        }

        /* Send event to the ULP.  'event' is the
         * sctp_ulpevent for  very first SKB on the  temp' list.
         */
        if (event)
            sctp_ulpq_tail_event(ulpq, event);
    }
}


/* Helper function to gather skbs that have possibly become
 * ordered by an an incoming chunk.
 */
static void sctp_ulpq_retrieve_ordered(struct sctp_ulpq *ulpq,
                          struct sctp_ulpevent *event)
{
    struct sk_buff_head *event_list;
    struct sk_buff *pos, *tmp;
    struct sctp_ulpevent *cevent;
    struct sctp_stream *in;
    __u16 sid, csid, cssn;

    sid = event->stream;
    in  = &ulpq->asoc->ssnmap->in;

    event_list = (struct sk_buff_head *) sctp_event2skb(event)->prev;

    /* We are holding the chunks by stream, by SSN.  */
    sctp_skb_for_each(pos, &ulpq->lobby, tmp) {
        cevent = (struct sctp_ulpevent *) pos->cb;
        csid = cevent->stream;
        cssn = cevent->ssn;

        /* Have we gone too far?  */
        if (csid > sid)
            break;

        /* Have we not gone far enough?  */
        if (csid < sid)
            continue;

        if (cssn != sctp_ssn_peek(in, sid))
            break;

        /* Found it, so mark in the ssnmap. */
        sctp_ssn_next(in, sid);

        __skb_unlink(pos, &ulpq->lobby);

        /* Attach all gathered skbs to the event.  */
        __skb_queue_tail(event_list, pos);
    }
}

/* Helper function to store chunks needing ordering.  */
static void sctp_ulpq_store_ordered(struct sctp_ulpq *ulpq,
                       struct sctp_ulpevent *event)
{
    struct sk_buff *pos;
    struct sctp_ulpevent *cevent;
    __u16 sid, csid;
    __u16 ssn, cssn;

    pos = skb_peek_tail(&ulpq->lobby);
    if (!pos) {
        __skb_queue_tail(&ulpq->lobby, sctp_event2skb(event));
        return;
    }

    sid = event->stream;
    ssn = event->ssn;

    cevent = (struct sctp_ulpevent *) pos->cb;
    csid = cevent->stream;
    cssn = cevent->ssn;
    if (sid > csid) {
        __skb_queue_tail(&ulpq->lobby, sctp_event2skb(event));
        return;
    }

    if ((sid == csid) && SSN_lt(cssn, ssn)) {
        __skb_queue_tail(&ulpq->lobby, sctp_event2skb(event));
        return;
    }

    /* Find the right place in this list.  We store them by
     * stream ID and then by SSN.
     */
    skb_queue_walk(&ulpq->lobby, pos) {
        cevent = (struct sctp_ulpevent *) pos->cb;
        csid = cevent->stream;
        cssn = cevent->ssn;

        if (csid > sid)
            break;
        if (csid == sid && SSN_lt(ssn, cssn))
            break;
    }


    /* Insert before pos. */
    __skb_queue_before(&ulpq->lobby, pos, sctp_event2skb(event));
}

static struct sctp_ulpevent *sctp_ulpq_order(struct sctp_ulpq *ulpq,
                         struct sctp_ulpevent *event)
{
    __u16 sid, ssn;
    struct sctp_stream *in;

    /* Check if this message needs ordering.  */
    if (SCTP_DATA_UNORDERED & event->msg_flags)
        return event;

    /* Note: The stream ID must be verified before this routine.  */
    sid = event->stream;
    ssn = event->ssn;
    in  = &ulpq->asoc->ssnmap->in;

    /* Is this the expected SSN for this stream ID?  */
    if (ssn != sctp_ssn_peek(in, sid)) {
        /* We've received something out of order, so find where it
         * needs to be placed.  We order by stream and then by SSN.
         */
        sctp_ulpq_store_ordered(ulpq, event);
        return NULL;
    }

    /* Mark that the next chunk has been found.  */
    sctp_ssn_next(in, sid);

    /* Go find any other chunks that were waiting for
     * ordering.
     */
    sctp_ulpq_retrieve_ordered(ulpq, event);

    return event;
}

/* Helper function to gather skbs that have possibly become
 * ordered by forward tsn skipping their dependencies.
 */
static void sctp_ulpq_reap_ordered(struct sctp_ulpq *ulpq, __u16 sid)
{
    struct sk_buff *pos, *tmp;
    struct sctp_ulpevent *cevent;
    struct sctp_ulpevent *event;
    struct sctp_stream *in;
    struct sk_buff_head temp;
    struct sk_buff_head *lobby = &ulpq->lobby;
    __u16 csid, cssn;

    in  = &ulpq->asoc->ssnmap->in;

    /* We are holding the chunks by stream, by SSN.  */
    skb_queue_head_init(&temp);
    event = NULL;
    sctp_skb_for_each(pos, lobby, tmp) {
        cevent = (struct sctp_ulpevent *) pos->cb;
        csid = cevent->stream;
        cssn = cevent->ssn;

        /* Have we gone too far?  */
        if (csid > sid)
            break;

        /* Have we not gone far enough?  */
        if (csid < sid)
            continue;

        /* see if this ssn has been marked by skipping */
        if (!SSN_lt(cssn, sctp_ssn_peek(in, csid)))
            break;

        __skb_unlink(pos, lobby);
        if (!event)
            /* Create a temporary list to collect chunks on.  */
            event = sctp_skb2event(pos);

        /* Attach all gathered skbs to the event.  */
        __skb_queue_tail(&temp, pos);
    }

    /* If we didn't reap any data, see if the next expected SSN
     * is next on the queue and if so, use that.
     */
    if (event == NULL && pos != (struct sk_buff *)lobby) {
        cevent = (struct sctp_ulpevent *) pos->cb;
        csid = cevent->stream;
        cssn = cevent->ssn;

        if (csid == sid && cssn == sctp_ssn_peek(in, csid)) {
            sctp_ssn_next(in, csid);
            __skb_unlink(pos, lobby);
            __skb_queue_tail(&temp, pos);
            event = sctp_skb2event(pos);
        }
    }

    /* Send event to the ULP.  'event' is the sctp_ulpevent for
     * very first SKB on the 'temp' list.
     */
    if (event) {
        /* see if we have more ordered that we can deliver */
        sctp_ulpq_retrieve_ordered(ulpq, event);
        sctp_ulpq_tail_event(ulpq, event);
    }
}

/* Skip over an SSN. This is used during the processing of
 * Forwared TSN chunk to skip over the abandoned ordered data
 */
void sctp_ulpq_skip(struct sctp_ulpq *ulpq, __u16 sid, __u16 ssn)
{
    struct sctp_stream *in;

    /* Note: The stream ID must be verified before this routine.  */
    in  = &ulpq->asoc->ssnmap->in;

    /* Is this an old SSN?  If so ignore. */
    if (SSN_lt(ssn, sctp_ssn_peek(in, sid)))
        return;

    /* Mark that we are no longer expecting this SSN or lower. */
    sctp_ssn_skip(in, sid, ssn);

    /* Go find any other chunks that were waiting for
     * ordering and deliver them if needed.
     */
    sctp_ulpq_reap_ordered(ulpq, sid);
}

static __u16 sctp_ulpq_renege_list(struct sctp_ulpq *ulpq,
        struct sk_buff_head *list, __u16 needed)
{
    __u16 freed = 0;
    __u32 tsn;
    struct sk_buff *skb;
    struct sctp_ulpevent *event;
    struct sctp_tsnmap *tsnmap;

    tsnmap = &ulpq->asoc->peer.tsn_map;

    while ((skb = __skb_dequeue_tail(list)) != NULL) {
        freed += skb_headlen(skb);
        event = sctp_skb2event(skb);
        tsn = event->tsn;

        sctp_ulpevent_free(event);
        sctp_tsnmap_renege(tsnmap, tsn);
        if (freed >= needed)
            return freed;
    }

    return freed;
}

/* Renege 'needed' bytes from the ordering queue. */
static __u16 sctp_ulpq_renege_order(struct sctp_ulpq *ulpq, __u16 needed)
{
    return sctp_ulpq_renege_list(ulpq, &ulpq->lobby, needed);
}

/* Renege 'needed' bytes from the reassembly queue. */
static __u16 sctp_ulpq_renege_frags(struct sctp_ulpq *ulpq, __u16 needed)
{
    return sctp_ulpq_renege_list(ulpq, &ulpq->reasm, needed);
}

/* Partial deliver the first message as there is pressure on rwnd. */
void sctp_ulpq_partial_delivery(struct sctp_ulpq *ulpq,
                struct sctp_chunk *chunk,
                gfp_t gfp)
{
    struct sctp_ulpevent *event;
    struct sctp_association *asoc;
    struct sctp_sock *sp;

    asoc = ulpq->asoc;
    sp = sctp_sk(asoc->base.sk);

    /* If the association is already in Partial Delivery mode
     * we have noting to do.
     */
    if (ulpq->pd_mode)
        return;

    /* If the user enabled fragment interleave socket option,
     * multiple associations can enter partial delivery.
     * Otherwise, we can only enter partial delivery if the
     * socket is not in partial deliver mode.
     */
    if (sp->frag_interleave || atomic_read(&sp->pd_mode) == 0) {
        /* Is partial delivery possible?  */
        event = sctp_ulpq_retrieve_first(ulpq);
        /* Send event to the ULP.   */
        if (event) {
            sctp_ulpq_tail_event(ulpq, event);
            sctp_ulpq_set_pd(ulpq);
            return;
        }
    }
}

/* Renege some packets to make room for an incoming chunk.  */
void sctp_ulpq_renege(struct sctp_ulpq *ulpq, struct sctp_chunk *chunk,
              gfp_t gfp)
{
    struct sctp_association *asoc;
    __u16 needed, freed;

    asoc = ulpq->asoc;

    if (chunk) {
        needed = ntohs(chunk->chunk_hdr->length);
        needed -= sizeof(sctp_data_chunk_t);
    } else
        needed = SCTP_DEFAULT_MAXWINDOW;

    freed = 0;

    if (skb_queue_empty(&asoc->base.sk->sk_receive_queue)) {
        freed = sctp_ulpq_renege_order(ulpq, needed);
        if (freed < needed) {
            freed += sctp_ulpq_renege_frags(ulpq, needed - freed);
        }
    }
    /* If able to free enough room, accept this chunk. */
    if (chunk && (freed >= needed)) {
        __u32 tsn;
        tsn = ntohl(chunk->subh.data_hdr->tsn);
        sctp_tsnmap_mark(&asoc->peer.tsn_map, tsn, chunk->transport);
        sctp_ulpq_tail_data(ulpq, chunk, gfp);

        sctp_ulpq_partial_delivery(ulpq, chunk, gfp);
    }

    sk_mem_reclaim(asoc->base.sk);
}



/* Notify the application if an association is aborted and in
 * partial delivery mode.  Send up any pending received messages.
 */
void sctp_ulpq_abort_pd(struct sctp_ulpq *ulpq, gfp_t gfp)
{
    struct sctp_ulpevent *ev = NULL;
    struct sock *sk;

    if (!ulpq->pd_mode)
        return;

    sk = ulpq->asoc->base.sk;
    if (sctp_ulpevent_type_enabled(SCTP_PARTIAL_DELIVERY_EVENT,
                       &sctp_sk(sk)->subscribe))
        ev = sctp_ulpevent_make_pdapi(ulpq->asoc,
                          SCTP_PARTIAL_DELIVERY_ABORTED,
                          gfp);
    if (ev)
        __skb_queue_tail(&sk->sk_receive_queue, sctp_event2skb(ev));

    /* If there is data waiting, send it up the socket now. */
    if (sctp_ulpq_clear_pd(ulpq) || ev)
        sk->sk_data_ready(sk, 0);
}